Process and apparatus for crushing hard or abrasive materials under high pressure without contamination of the ground product

ABSTRACT

Crushing apparatus and method: two secondary rollers, vertically stacked and spaced apart; a primary roller pressed sideways against and into the space between the secondary rollers; particles to be crushed pass first between the upper secondary and primary rollers, then fall freely to the space between the lower secondary and primary rollers and then pass between the latter rollers to be recrushed; pressure roller presses against primary roller; disclosure relates to roller size, roller materials, roller orientations and roller pressures.

United States Patent [191 [111 3,910,506

Pecci [451 Oct. 7, 1975' [54] PROCESS AND APPARATUS FOR 3,066,876 12/1962 Verdier 241/230 X CRUSHING HARD OR ABRASIVE MATERIALS UNDER HIGH PRESSURE WITHOUT CONTAMINATION OF THE GROUND PRODUCT Inventor: Carlos Romeu Y Pecci, l-listoriador Diago No. 14, Valencia, Spain Filed: Apr. 30, 1974 Appl. No.: 465,701

Related U.S. Application Data Continuation-in-part of Ser. No. 305,876, Nov. 13, 1972, abandoned.

Foreign Application Priority Data Nov. 11, 1971 Spain 396921 U.S. Cl. 241/29; 241/159; 241/230 Int. Cl. B02C 4/32 Field of Search 241/29, 111, 113, 117, 241/118,119, 120, 121, 122, 152,157, 158, 159, 221, 227, 229, 230, 231, 232, 233, 234, 235

References Cited UNITED STATES PATENTS 1/1889 Gent 241/111 X FOREIGN PATENTS OR APPLlCATIONS 538,805 3/1957 Canada 241/231 911,395 11/1962 United Kingdom 241/159 Primary Examiner-Granville Y. Custer, Jr. Attorney, Agent, or Firm-0str0lenk, Faber, Gerb & Soffen [57] ABSTRACT Crushing apparatus and method: two secondary rollers, vertically stacked and spaced apart; a primary roller pressed sideways against and into the space between the secondary rollers; particles to be crushed pass first between the upper secondary and primary rollers, then fall freely to the space between the lower secondary and primary rollers and then pass between the latter rollers to be recrushed; pressure roller presses against primary roller; disclosure relates to roller size, roller materials, roller orientations and roller pressures.

16 Claims, 19 Drawing Figures US. Patent Oct. 7,1975 Sheet 1 of 6 3,910,506

FIGJ

FIG.2

US. Patent Oct. 7,1975 Sheet 2 of6 3,910,506

US. Patent Oct. 7,1975 Sheet 3 of 6 3,910,506

US. Patent Oct. 7,1975 Sheet4 0f6 3,910,506

US. Patent Oct. 7,1975 Sheet 5 of6 3,910,506

US. Patent Oct. 7,1975 Sheet 6 of6 3,910,506

PROCESS AND APPARATUS FOR CRUSI-IING HARD OR ABRASIVE MATERIALS UNDER HIGH PRESSURE WITHOUT CONTAMINATION OF THE GROUND PRODUCT BACKGROUND OF THE INVENTION This is a continuation-in-part of application Ser. No. 305,876, filed Nov. 13, 1972, now abandoned.

Comminution is tranformation of particles of a hard material into a greater number of smaller size particles by any of the processes of crushing, grinding or milling.

In order to understand the present invention, it is necessary to define the various techniques of comminution. In crushing, to which the present invention is directed, working force is applied to transform the material only by compression. In certain applications, the object performing the crushing may not be as-hard as the material being crushed. In grinding, the object performing the grinding is harder than the material being ground and the grinding is accomplished under elevated mechanical pressure. The speeds of movement of the material being ground and of the object performing the grinding are different. Grinding and crushing oper ations, especially using rollers, are sometimes confused. But, they are quite different, In milling or calendering, the material being milled is destroyed under pressure and is at the same time spread out in order to obtain the desired fineness of the material. Milling is accomplished between two facing milling surfaces whose relative speeds are different.

Comminution has evolved from fragmentation by impact, i.e. a person uses a club or rudimentary hammer to strike the materials to be comminuted, to automatic procedures and apparatus. At the present state of technology, for virtually all hard comminutable materials, there exists an appropriate type of Comminution apparatus that is suited to the characteristics of the material to be comminuted. These apparatus include specific types of automatic or autogenous grinders, crushers, reduction crushers, breakers, roller mills, hammer mills, etc. However, not all such apparatus operate economically or efficiently and not all utilize energy optimally. In addition, many of these apparatus and processes using these apparatus require subsequent procedures to be performed upon the comminuted material, e.g. acid or chemical baths, washing, decanting, magnetic separation, etc., in order to eliminate contaminants and/or to remove impurities that were picked up by the material during Comminution, particularly as a result of the operating characteristics of the comminuting apparatus.

One of the situations for which there has not previously existed a satisfactory Comminution technique is the fine fragmentation of hard materials whose particles before Comminution are less than 0.5 mm. across, particularly when these particles have abrasive characteristics, for example corundum, silicone carbide, emery, grog, calcined bauxite, etc. Systems for comminuting such materials have principally used crushers which are based upon two parallel, elongated rollers with engaging peripheral surfaces between which materials are passed and crushed. In order to crush the material to the desired degree of fineness, it is necessary to increase the pressure between the two rollers, in accordance with the laws of Rittinger, Kick, Bond andlater investigators.

In the foregoing systems, the force needed to cause the rollers to exert pressure is applied to the rollers through the roller support bearings at the axial ends of the rollers. This concentrates the working force at the ends of the rollers. According to the nature of the material being crushed, such concentration causes roller deformation through flexion, which produces premature wear of the rollers at their ends or, if the rollers are of small diameter, produces wear at the central areas of the rollers, especially if the resistance of the material to be crushed is greater than the force necessary to overcome the rigidity of the crushing rollers. This fact limits the minimum diameters of the rollers.

Even with very high working'pressures between the surfaces of the two rollers and even with properly dimensioned rollers, because the material to be comminuted or crushedconsists of particles of non-uniform size, some of the larger particles protrude outwardly more than the smaller particles. The crushing rollers press against the protruding larger particles and tend to break up only these larger particles.

All comminutable material that is fed into a crusher necessarily has a large number of spaces or voids between the particles. To understand the effect of the voids, with synthetic corundum that has been ground to 0.5 mm., the apparent density of the ground material is 1.5 gr./cm while the actual density of such material, if it had no voids, would be 3.9 gr./cm.

When the larger size particles are crushed, the particles crack and shift in position and, coupled with the uncrushed particles of smaller size, form a now void free, more homogeneous, compacted layer, which acts like a mattress to absorb the crushing pressure of the rollers and limits the crushing effect of the rollers or other crushing means. Therefore, in a single pass of particles between two crushing rollers, the nature of the particles inherently limits the extent of crushing and the size to which the particles can be crushed.

Materials subject to the foregoing mattress effect include materials that, before crushing, had been sieved in square mesh sieves and include fine materials for which the apparatus of the present invention is designed. In such square mesh sieves, the particle size differences can reach the proportion 1:1.41, which is the length difference that exists between the side and the diagonal of each opening through the square mesh, whereby it is clear that different size particles will be involved in the crushing regardless of efforts to make the particles that are to be ground uniform in size.

Because of the above described effects, the diameters of the rollers of a crushing means become important. Considering the circular section of a roller as the ultimate limit form acquired by a regular polygon of very short length sides, it is apparent that the smaller the roller diameter, the shorter in length is each portion of the roller periphery that may be considered a straight side of the polygon. Conversely, the greater the roller diameter, the greater also is the dimension of each portion of the periphery that may be considered a straight side thereof. Transferring these considerations to crushing rollers, with very large diameter rollers, the crushing process is quite similar to crushing an object between two planes, whereas in the case of small rollers, the crushing process is similar to crushing material between facing cutting edges or surfaces. As a result of the foregoing, with large main grinding rollers, the

above mentioned mattress like layer is more likely to be formed and the crushed particles obtained are likely to include a larger proportion of larger particles. On'

the other hand, very small rollers not only makes formation of the mattress like compacted layer more difficult, but any layer so formed is almost cut by the generatrix of the rollers, and the crushing produces finer particles of a smaller size than the large roller crushing.

The traditional solution to the foregoing problem is to pass material to be crushed through successive sets of crushing rollers. After each crushing stage, the fine particles obtained are sieved. This breaks up the compacted layer, loosens the particles, recreates voids and facilitates the next stage of crushing. It has been known to install up to three and four sets of crushing rollers in series, with intermediate sieving. A variation of the foregoing procedure involves recycling of the previously crushed material through the same crushing rollers with sieving after each crushing stage. The disad vantages of the foregoing traditional system include the necessity of sieving between each crushingstage and the necessity for providing a series of separately operated crushing rollers or means.

To avoid the foregoing disadvantages, when very finely comminuted materials are required, impact crushing, involving hammer, rod or ball mills is resorted to. However, with very hard or abrasive materials, this has the disadvantage of rapid wearing of the hammers, rods or balls. The wearing in turn produces contamination of the crushed material which necessitates a later treatment. According to the purity of the crushed material required, later treatment could extend to chemical washing with acid, as with white synthetic corundum used for the manufacture of abrasive grindstones and oxide ceramics used in the optical industry.

The modern vibration mill technique is an improved variation on the ball mills. However, it produces less contamination of the crushed material only when the mill is internally coated with plates or sections of the materials to be crushed and only when the crushing balls are also of that same material in sintered form. This makes the process quite costly and inefficient because the vibratiorr impact is limited by the size of the balls used.

Jet milling should be mentioned. Material to be crushed is projected against itself in two pressure forced streams. The pressure is supplied by compressed air or steam. When abrasive materials are jet milled, contamination occurs through the friction of the material with the means conveying it to the impact and with the outlet means from the jet milling installation. However, the greatest disadvantage of this procedure is the large quantity of compressed fluid that must be provided and the enormous pneumatic pressures at which the system must operate to reduce the particles to the desired small size. This system has the disadvantage that where very fine materials are to be produced, it is more economical to use the throwing or ball mills or impact crushers with subsequent impurity removal treatment than to use jet milling.

SUMMARY OF THE INVENTION One of the principal reasons that the apparatus and process of the present invention minimizes the presence of contaminants in the crushed material is that the material is crushed and the crushing surfaces do not grind or mill the material while they are crushing it. Contamination occurs with grindingor milling due to rubbing together of the grinding or milling surfaces and rubbing together of the material being ground and the grinding or milling surfaces.

In accordance with the present invention, comminutable material is crushed successively between the surfaces of a main and first secondary crushing roller and then between the surfaces of the main and another secondary crushing roller. All three rollers have the same peripheral velocity and therefore no contamination of the crushed material occurs.

In the first phase of crushing, material to be crushed is fed onto the main crushing roller along the axis and across the whole width of its surface. It forms a continuous layer, passes between the main and the first'of the secondary crushing rollers and is crushed. Because of the above described mattress like layer that is formed as a result of the crushing, it is mainly the larger size particles which are comminuted.

The main crushing roller is of a relatively smallerdiameter and it is situated in a vertical plane between the two other crushing rollers of greater diameter. No sieving of the material that has passed through the first crushing is necessary because, as a result of the resilience of the steel used for the rollers, the small diameter of the main crushing roller and the peripheral speed of the rollers, the crushed materialdoes not form the mattress like layer after it has passed through the first phase of crushing. The material is instead caused to spring away from the main crushing roller and to fall loose and freely along the entire width of the main crushing roller and in contact with the surface of the other large diameter secondary roller situated below the first mentioned large diameter secondary roller.

The second crushing phase occurs between the main and lower secondary crushing roller. These rollers receive a material which is much more homogeneous with respect to particle size and which is virtually without any compaction. In the second crushing phase,

using the necessary pressure, the desired particle size is obtained.

The process and apparatus for performing it which are the subject of the present invention were designed after studies carried out by the inventor to determine, using rollers or cylinder-type crushing mills, the interdependence and the effect upon the material produced by crushing through modifying the following variables: (a) the number of crushing rollers; (b) the diameters of the crushing rollers; (c) the forces applied to these crushing rollers and thus the pressures applied by these rollers; (d) the speed of rotation of the peripheries of the rollers; (e) the hardness of the rollers; and (f) the rate at which material to be crushed is dispensed or fed to the rollers.

Once the appropriate roller resilient material, roller peripheral speed and number of rollers has been establi'shed, they are not varied in normal use of the apparatus and it is only the below described three factors which are varied.

It has been experimentally proven that by appropriate variation within fixed limits of the variable factors of roller pressure, roller diameter and rate of flow of material to the rollers, a fine crushed material may be obtained having identical characteristics from the viewpoint of its granular form and the percentage distribu tion of various size particles along the granulometric curve, generally known as the granulometric spectrum of the product.

By increasing the diameter of the main crushing roller, final crushed particles are obtained which are of greater size. By reducing the diameter of this roller, very fine particles are obtained. Experimenting with white synthetic corundum, grinding finenesses of 0.003mm. have been obtained.

By increasing the working pressure of the main crushing roller, a greater proportion of fine particles is obtained, and conversely, at lower crushing pressures, a lesser proportion is obtained.

By appropriately modifying the flow rate or rate at which material to be crushed is fed to the apparatus, the width of the granulometric spectrum can be varied. With a higher flow rate, the spectrum begins almost at the original large size of the material to be crushed and ends with the material being of a size of the fineness which is dictated by the chosen diameter of the main crushing roller. By decreasing the flow rate, the width of the granulometric spectrum is reduced, and the spectrum begins at a particle size more close to the finest particle size produced by crushing, again within the limits dictated by the selected diameter of the main crushing roller.

One problem experienced with elongated rollers used for crushing is that as larger particles move between rollers, they momentarily raise one of the rollers away from the other and the previously parallel axes of these two rollers are twisted oblique with respect to each other. Where a crushing system involves only two coacting rollers, although the axes of the rollers shift, the mutual crushing force will still be exerted along the entire width of these rollers along their axes.

With a three roller system, employing one main crushing roller and two cooperatingly spaced secondary rollers, the raising of the main crushing roller off the first of the secondary crushing rollers causes the respective axes of the main and first secondary rollers to be oblique (and causes their axes, if they were extended, to meet a considerable distance from the apparatus), but the mutual crushing force is still exerted along the entire width of these rollers. However, the respective axes of the main and the second of the secondary crushing rollers twist with respect to each other (causing their axes to cross at the rollers), such that instead of the main and second secondary roller surfaces being in engagement over their entire width, only a short width portion of the peripheral surfaces will be in engagement. This interrupts the crushing operation being performed by the main crushing roller and the second secondary crushing roller.

In order to minimize that undesirable raising of the main roller with respect to one of the secondaryrollers which causes the undesirable twisting of the main roller with respect to the other secondary roller, the size of the main roller with respect to the secondary roller, the angular location around the secondary rollers of the two respective points of contact of the main roller with the secondary rollers, the included angle defined by the axes of the main and two secondary rollers and the pressure applied to the main roller to force it against the secondary rollers are all selected so as to minimize the raising of the main crushing roller off the secondary rollers and to cause such raising, which is unavoidable, to be such that there is no, or at most minimal, twisting of the axis of the main roller with respect to the axes of the secondary rollers. I

For exerting the necessary high pressure upon the main roller to enable it to crush material against both the secondary rollers and to reduce or eliminate the undesired twisting of the main roller axis, the main roller is forced against the secondary rollers by a separate pressure roller with a parallel axis. In addition, as noted above, in order to crush sufficiently fine particles, it may be necessary to have the main crushing roller of small diameter. A small diameter roller may undesirably flex under the high crushing pressures. The pressure roller extending along the full width of the main crushing roller will rigidify the undesirably more flexible main roller.

Accordingly, it is the primary object of the present invention to efficiently comminute materials.

It is another object of the present invention to comminute materials with minimal contamination.

' It is a further object of the invention to comminute the materials in a single continuous process using a single comminuting roller apparatus.

It is a further object of the present invention to accomplish such comminution by crushing.

It is yet another object of the present invention to provide a process and an apparatus for crushing wherein the granulometric spectrum of the comminuted material may be readily adjusted by simple modifications in certain operating conditions.

It is a further object of the present invention to enable the performance of plural crushing procedures on comminutable material without intermediate sieving procedures.

It is another object of the present invention to enable plural crushing procedures to be performed using a single main crushing roller.

These and other objects of the present invention will become apparent from the following description of the accompanying drawings which shows a non-limitative example of the process and apparatus of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 and 2 show a traditional prior art comminut ing system;

FIG. 3 shows typical granulated comminutable material prior to comminution;

FIG. 4 shows the same material after comminution by crushing; 7

FIGS. 5 and 5a demonstrate the effect of crushing by a relatively larger area crushing surface;

FIGS. 6 and 6a demonstrate the effect of crushing by a relatively smaller area crushingsurface;

FIG. 7 is a schematic perspective view of a crushing apparatus in accordance with the invention;

FIG. 7a is a schematic illustration of the appartus of FIG. 7 showing the points of contact of the various crushing means;

FIG. 7b schematically shows the apparatus of FIG. 7 in use;

FIGS. 8, 9, 10, 1 1, 12, 13, 14 and 15 graph various granulometric distribution, spectra with the proportion of all of the ground material being represented on the ordinate and with the ground grain size being represented on the abscissa, with the grain size being larger moving toward the origins. All graphs are in the same proportion and have the same quantity numerals along their axes.

DETAILED DESCRIPTION OF THE INVENTION In FIGS. 1 and 2, a more conventional crushing system is illustrated. There are two engaging rollers l, 2 between which the material 3 to be crushed circulates. The fineness to which the material 3 is crushed depends upon the pressure exerted by rollers 1 and 2, which pressure is regulated with control unit 4. However, an increase in the pressure concentrates the operative forces at the axial ends of rollers 1, 2 with the resulting disadvantages discussed above.

FIG. 3 shows particles 5 of the material to be crushed before it is crushed. The particles are of various sizes, some relatively quite large. Because of the irregular size and shape of the particles and their quantity, they can never align with each other, surface to surface, whereby numerous voids 6 are inherently formed be tween neighboring particles.

As shown in FIG. 4, particles 5 have been crushed, the large particles 5 are broken up and the voids are filled by reorientation of particles, by the particles being broken up and crushed together. The resulting flattened, relatively void free layer of FIG. 4 has a mattress like effect in resisting any further crushing by any crushing means. The present invention overcomes the problem of the mattress like layer produced in a single crushing operation, whereby the present invention permits plural crushing steps without sieving of the particles to reorient them, loosen them and recreate the condition of FIG. 3 before each successive grinding procedure.

Turning to FIGS. 5 and 5a, if the diameter of roller 7 in FIG. 5a is large, the crushing performed on comminutable materials between roller 7 and the surface which it opposes would be similar to the crushing that would be obtained in FIG. 5 on the large body 8 that is placed between two flat surfaced crushing elements 9, 10.

Turning to FIGS. 6, 6a, if the roller 11 is of smaller diameter, as compared with the roller 7, as shown in FIG. 6, the crushing performed on the material between roller 1 1 and the surface which it opposes is similar to the crushing that would be obtained in FIG. 6 on the large object 12 which is situated between cutting edges 13 and the surface beneath object 12.

As a result, the smaller is the diameter of one of the crushing rollers, the finer are the particles produced in the crushing process.

The apparatus in accordance with the invention, shown in FIGS. 7, 7a and 7b, makes use of the above understanding.

Summarizing the elements of which an apparatus in accordance with the invention is comprised and which performs a process in accordance with the invention, FIG. 7 shows a main crushing roller 14 which is positioned between and is forced by pressure roller 15 against an upper secondary crushing roller 16a and a lower secondary crushing roller 16]). The axes of all of the rollers are generally parallel.

The three crushing rollers are comprised of a hard, yet resilient, steel. The hardness must always be greater than 50 Rockwell C. The roller resilience enables the roller surfaces to be minutely depressed as the particles are crushed. Just past the crushing line, the roller material elasticity springs the crushed particles off the rollers and causes the material to fall in the more random pattern of FIG. 3 rather than in the more usual mattress like crushed material layer of FIG. 4. The resilience of the steel is selected from an economic point of view according to the hardness required, the hardness and abrasiveness of the material to be crushed and the expected working pressure.

The theoretical peripheral velocities of all four rollers 14, 15, 16a, 16b is the same and is generally between 5 and 9 meters/see, a higher velocity corresponding to a more resilient steel. In addition to the resilience of the rollers, the peripheral speed of the rollers will centrifugally throw the particles away from the roller.

The diameter of main crushing roller 14 is selected. to obtain the desired ground particle size, as discussedv in connection with FIGS. 5a and 6a. The most suitable diameter for the main crushing roller is in the range of from to 250mm. Furthermore, the secondary rollers 16a, 16b are generally of a larger diameter, e.g. 1.5 to 4 times greater than the diameter of the main crushing roller to obtain the maximum benefit from the pressure being applied by main roller 14. As the diameter of main roller 14 increases with respect to the diameters of the secondary rollers, the main roller component of force that is useful in crushing material decreases, other factors remaining unchanged, whereby a smaller relative size for the main roller is preferred. The working pressures vary, according to the material to be crushed and according to the diameter of the main crushing roller 14, in a range of from 12 to 250kg./linear centimeter of the width of main roller 14.

The working pressure applied by relatively smaller main roller 14 is applied to that roller along its entire width through roller 15, which is oversize with respect to roller 14 and which engages it along their respective entire widths. Pressure roller 15 may be as robust'as necessary. Using pressure roller 15 to apply pressure along main crushing roller 14 avoids the undesirable flexing and particle caused raising and twisting of the main crushing roller and permits the main roller to be made with as small a diameter as may be required. Pressure roller 15 receives the working pressure through its axis 17 by means of a conventional hydraulic pressure exerting mechanism 18. Pressure roller 15 moves in its own horizontal working plane along appropriate guidelines (not shown) and perpendicularly to its axis 17 in order to enable roller 15 to adapt to different diameter main and secondary rollers.

Secondary rollers 16, 16a have the greatest diameter, are designed with the necessary robustness and are fixed to the frame of the apparatus. Their axes 22, 25 are oriented generally parallel to each other and the rollers themselves are disposed generally vertically one directly above the other.

The size, spacing and relative positions of the main andsecondary rollers are selected to effectively maximize the component of force exerted by the main roller for the purpose of crushing materials, as discussed above, and also to minimize the chance that the main roller will twistingly raise off the surface of one of the secondary rollers to undesirably twist with respect to the other secondary roller, as discussed above. The presence of pressure roller 15 which engages main roller 14 along its entire length greatly helps in inhibiting the twisting. In addition, the high operating pressures exerted upon roller 14 inhibit twisting. Main roller 14 i is in a cage defined by secondary rollers 16a, 16b and pressure roller 15, which minimizes the shifting or twisting movement of main roller 14.

Furthermore, the included angle a defined by the axes of secondary rollers 16a, 16b and of main roller 14 preferably exceeds 90. This moves the lines of contact a. b (FIG. 7a) between main roller 14 and respective secondary rollers 16a, 16b relatively closer to the line joining the axes of rollers 16a, 16b for also inhibiting the raising of roller 14 off one of the secondary rollers 16a, 16b. But, the points of contact a, b are not so far toward the line joining the secondary roller axes as to prevent particles crushed at point a from falling past roller 14 toward point b. To ensure that the crushed particles fall from point a to point b, the size and location of the rollers is selected so that roller 14 does not project across the line joining the axes of secondary roller 16a, 16b.

All of the foregoing is designed so that it takes a greater effort to undesirably twist main roller 14 than it does for that roller to crush particles, whereby the particles are crushed rather than causing the main roller to twist.

The apparatus in FIG. 7 is operated by an electric motor 19, which is belt connected with pulley 21 on axis 22. A belt drive passes around all of the axes of secondary rollers 16a, 16b and pressure roller 15. All of rollers 15, 16a and 16b should have the same peripheral velocity and this can be obtained by appropriately sizing the pulleys on each of the respective roller axes and by providing an appropriate fluid coupling at the axes of each of rollers 15 and 16b in the event of any minor or transient roller speed discrepancies.

This fluid coupling allows slight differences of rotative velocity between the driving element axis 22 and the rollers 15, 16a and 16b, which it operates. This is to compensate for slight differences in diameter which could become necessary as, through inclusion of hard foreign bodies or through carelessness in regulating the working pressure of the machine, the machine has working pressures below those .required for proper contact driving of the main roller 14, or if one of the rollers on the machine has worn, or if it had become necessary to turn and correct any of the rollers.

Main crushing roller 14 is not directly driven by any motor. Owing to the workingconditions required and to the nature of the material being crushed, roller 14 is driven through frictional engagement with all of secondary rollers 16a, 16b and pressure roller 15, which are operated as above described. I

The nature of the drive for main roller 14 and the requirement that the rollers not slide with respect to each other puts a theoretical size limitation on the particles to be crushed. The maximum size particles to be crushed are rather fine because the particles being initially ground must be sufficiently fine to provide a suffi' ciently large number of points of contact between the main roller 14 and the first secondary roller 16a to frictionally cause roller 14 to operate. If the particles are initially too large, (a theoretical extreme would be but one large particle,) there would be too few points of contact to cause proper rotation of roller 14. The maximum starting size for particles before crushing is about 0.3 mm. for fused alumina (corundum), for example.

FIG. 7b shows that when roller 14 rotates counter clockwise in FIG. 7b, it forces material between roller 14 and upper secondary roller 16a, which rotates clockwise, and thereafter between main roller 14 and lower secondary roller 16b, which rotates clockwise. Pressure roller 15 also rotates clockwise.

If the appropriate pressures and roller diameters have been selected, no control sieving of the ground particles after either of the grinding procedures is necessary.

As is implied by FIG. 7b, the thickness of the layer of material to be crushed at point a between rollers 14 and 16a is different from the thickness of the layer of previously crushed material, which is to be crushed at point b between rollers 14 and 16b. In the course of its work in crushing various size particles and in passing these particles past points a and b, main roller 14 has been observed to shift along a generally elliptically shaped pathway transverse to its axis. For this reason, roller 14 is guided axially only by means of specially designed bearings, which permit such elliptical shifting.

Returning to FIG. 7, the outflow of material past point b falls into hopper l9 and is transmitted from there to a storage location in the usual manner.

As was noted above, with the apparatus of the inven' tion, variations in the diameter of the main crushing roller, the working pressure applied by that roller and- /or the rate at which material is fed to point a and thus the rate of flow of the material control the granulometric spectrum. Drawing FIGS. 8 to 15 deal with variations in these factors.

FIG. 8 depicts a granulometric spectrum obtained with a relatively large main roller 14, a relatively low working pressure and a relatively reduced rate of feeding to point a.

The spectrum of FIG. 9 was obtained by further reducing the working pressure as compared with the spectrum of FIG. 8, without disturbing the other factors.

The spectrum of FIG. 10 was obtained by increasing the rate of feeding to point a as compared with the spectrum of FIG. 8, without disturbing the other factors.

The spectrum of FIG. 11 was obtained with an apparatus having a large main roller, a relatively high working pressure and a relatively high flow rate of feed rate to point a.

The spectrum of FIG. 12 was obtained with a relatively small main roller, but with the other factors being the same as with the spectrum of FIG. 8.

The spectrum of FIG. 13 was obtained with a high workingpressure for the main roller but with other factors being the same as with the spectrum of FIG. 12.

The spectrum of FIG. 14 was obtained with a high rate of feed to point a but with other factors being the same as with the spectrum of FIG. 12.

The spectrum of FIG. 15 was obtained with a small roller, a high rate of feed and a high working pressure.

Although the present invention has been described in connection with a preferred embodiment thereof, many variations and modifications will now become apparent to those skilled in the art. It is preferred, therefore, that the present invention be limited not by the specific disclosure herein, but only by the appended claims.

I claim:

1. Apparatus for crushing particulate materials, comprising:

a primary crushing roller of a first diameter, said primary roller having an axis which is generally horizontal and said primary roller having a peripheral surface;

two secondary rollers, saidsecondary rollers each having an axis parallel to said primary roller axis, and each having a respective peripheral surface which is in engagement with said primary roller peripheral surface; said secondary roller peripheral surfaces being spaced apart a first distance less than said first diameter; said secondary rollers being located one above the other and being located such that materials passing between said primary and upper said secondary rollers will fall and be directed by rotation of said rollers to move between said primary and the lower said secondary rollers;

means for rotating said rollers about their respective said axes to direct the material to move between the upper said secondary roller and said primary roller and thereafter to move between the lower said secondary roller and said primary roller;

a pressure roller having an axis parallel to said primary roller axis, said pressure roller having a peripheral surface that is positioned to engage said primary roller peripheral surface and said pressure roller being located so as to apply pressure to force said primary roller peripheral surface against said secondary roller peripheral surfaces; means for biasing said pressure roller against said primary roller;

rotation means connected with all of said secondary and said pressure rollers for rotating them in the same direction and for causing them to all rotate at the same peripheral speed; said means for rotating said primary roller comprises said pressure and said secondary rollers which are in engagement with said primary roller.

2. Apparatus for crushing particulate materials, comprising:

a primary crushing roller of a first diameter, said primary roller having an axis which is generally horizontal and said primary roller having a peripheral surface;

said primary roller being comprised of resilient material, which is depressed as material to be crushed passes between said primary and an upper secondary roller and which resiliently restores itself after ward to expel the crushed material from said primary roller;

two secondary rollers, said secondary rollers each having an axis parallel to said primary roller axis, and each having a respective peripheral surface which is in engagement with said primary roller peripheral surface; said secondary roller peripheral surfaces being spaced apart a first distance less than said first diameter; said secondary rollers being located one above the other and being located such that materials passing between said primary and the upper said secondary rollers will fall and be directed by rotation of said rollers to move between said primary and the lower said secondary rollers;

means for rotating said rollers about their respective said axes to direct the material to move between the upper said secondary roller and said primary roller and thereafter to move between the lower said secondary roller and said primary roller:

a pressure roller having an axis parallel to said primary roller axis, said pressure roller having a peripheral surface that is positioned to engage said primary roller peripheral surface and said pressure roller being located so as to apply pressure to force said primary roller peripheral surface against said secondary roller peripheral surfaces; means for bi asing said pressureroller against said primary roller.

3. The crushing apparatus of claim 2,, wherein said primary roller is made of steel of a hardness greater than 50 Rockwell C.

4. The crushing apparatus of claim 3, wherein said secondary rollers are also of resilient steel of a hardness greater than 50 Rockwell C. k

5. The crushing apparatus of claim 2, wherein said roller rotation means rotates said rollers at a peripheral velocity that is in the rangerof 5 to 9 meters/sec.

6. Apparatus for crushing particulate materials, comprising:

a primary crushing roller of a first diameter, said pri mary roller having an axis which is generally horizontal and said primary roller having a peripheral surface;

two secondary rollers, said secondary rollers each having an axis parallel to, said primary rolleraxis,

and each having a respective peripheral surface which is in engagement with said primary roller peripheral surface; said secondary roller peripheral surfaces being spaced apart a first distance less than said first diameter; said secondary rollers being located one above the other and being located such that materials passing between said primary and the upper said secondary rollers will fall and be directed by rotation of said rollers to move between said primary and the lower said secondary rollers;

means for rotating said rollers about their respective said axes to direct the material to move between the upper said secondary roller and said primary roller and thereafter to move between the lower said secondary roller and said primary roller;

said primary roller axis being offset from a line joining said secondary roller axes; said first distance between said secondary rollers and said primary roller first diameter being selected so that said primary roller peripheral surface extends toward, but does not cross, the line joining said secondary roller axes;

the angle defined by the upper said secondary roller axis, said primary roller axis and the lower said sec- I LII which is depressed as material to be crushed passes between said primary and an upper secondary roller and which resiliently restores itself afterward to expel the crushed material from said primary roller;

two secondary rollers, said secondary rollers each and each having an axis parallel to said primary rol ler axis, and each having a respective peripheral surface which is in engagement with said primary roller peripheral surface; said secondary roller peripheral surfaces being spaced apart a first distance less than said first diameter; said secondary rollers being located one above the other and being located such that materials passing between said primary and the upper said secondary rollers will fall and be directed by rotation of said rollers to move between said primary and the lower said secondary rollers;

means for rotating said rollers about their respective said axes to direct the material to move between the upper said secondary roller and said primary roller and thereafter to move between the lower said secondary roller and said primary roller.

9. The crushing apparatus of claim 8, whereinsaid roller rotation means rotates said rollers at a peripheral velocity that is in the range of to 9 meters/sec.

10. The crushing apparatus of claim 9, wherein said primary roller is made of steel of a hardness greater than 50 Rockwell C., said secondary rollers also being of resilient steel of a hardness greater, than 50 Rockwell C.

11. The crushing apparatus of claim 10, wherein the angle defined by the upper said secondary roller axis, said primary roller axis and the lower said secondary roller axis is greater than 90.

12. A process for crushing particles of hard material comprising the steps of:

providing two parallel vertically spaced apart secondary rollers and a primary roller disposed adjacent the space between the secondary rollers and contacting both of them; forcing the primary roller simultaneously against both secondary rollers; rotating the primary roller in a direction which moves material between the primary and upper secondary roller; rotating the secondary rollers in the opposite direction;

feeding material to be crushed at a predetermined flow rate to a location from which it can move between the upper secondary and primary rollers; crushing that material between the upper secondary and primary rollers;

throwing the crushed material off the primary roller after the material to be crushed has moved between the upper secondary and primary rollers; causing the crushed material to fall between the primary and lower secondary rollers and crushing this material a second time between the latter rollers.

13. The process for crushing material of claim 12, wherein the primary and secondary rollers are rotated at the same peripheral velocity.

14. The process for crushing material of claim 13, wherein the crushed material is thrown from the pri mary roller by selecting a primary roller of sufficient resiliency and by selection of a roller peripheral speed coordinated with the roller resiliency to be sufficient to throw off the material.

15. The process for crushing material of claim 14, wherein the roller peripheral velocity is in the range of from 5 to 9 meters/sec.

16. The process for crushing material of claim 14, wherein the granulometric spectrum of the particles produced by crushing is adjusted first by selecting an appropriate hardness and resilience for the roller material and by selecting an appropriate number of rollers and by selecting a predetermined rotation speed for the rollers and thereafter by performing only at least one of the steps ofzlchanging the diameter of the primary roller with respect to the diameter of the secondary rollers, changing the pressure exerted by the primary roller and changing the rate of feed of particles of material to the primary and upper secondary roller. 

1. Apparatus for crushing particulate materials, comprising: a primary crushing roller of a first diameter, said primary roller having an axis which is generally horizontal and said primary roller having a peripheral surface; two secondary rollers, said secondary rollers each having an axis parallel to said primary roller axis, and each having a respective peripheral surface which is in engagement with said primary roller peripheral surface; said secondary roller peripheral surfaces being spaced apart a first distance less than said first diameter; said secondary rollers being located one above the other aNd being located such that materials passing between said primary and upper said secondary rollers will fall and be directed by rotation of said rollers to move between said primary and the lower said secondary rollers; means for rotating said rollers about their respective said axes to direct the material to move between the upper said secondary roller and said primary roller and thereafter to move between the lower said secondary roller and said primary roller; a pressure roller having an axis parallel to said primary roller axis, said pressure roller having a peripheral surface that is positioned to engage said primary roller peripheral surface and said pressure roller being located so as to apply pressure to force said primary roller peripheral surface against said secondary roller peripheral surfaces; means for biasing said pressure roller against said primary roller; rotation means connected with all of said secondary and said pressure rollers for rotating them in the same direction and for causing them to all rotate at the same peripheral speed; said means for rotating said primary roller comprises said pressure and said secondary rollers which are in engagement with said primary roller.
 2. Apparatus for crushing particulate materials, comprising: a primary crushing roller of a first diameter, said primary roller having an axis which is generally horizontal and said primary roller having a peripheral surface; said primary roller being comprised of resilient material, which is depressed as material to be crushed passes between said primary and an upper secondary roller and which resiliently restores itself afterward to expel the crushed material from said primary roller; two secondary rollers, said secondary rollers each having an axis parallel to said primary roller axis, and each having a respective peripheral surface which is in engagement with said primary roller peripheral surface; said secondary roller peripheral surfaces being spaced apart a first distance less than said first diameter; said secondary rollers being located one above the other and being located such that materials passing between said primary and the upper said secondary rollers will fall and be directed by rotation of said rollers to move between said primary and the lower said secondary rollers; means for rotating said rollers about their respective said axes to direct the material to move between the upper said secondary roller and said primary roller and thereafter to move between the lower said secondary roller and said primary roller: a pressure roller having an axis parallel to said primary roller axis, said pressure roller having a peripheral surface that is positioned to engage said primary roller peripheral surface and said pressure roller being located so as to apply pressure to force said primary roller peripheral surface against said secondary roller peripheral surfaces; means for biasing said pressure roller against said primary roller.
 3. The crushing apparatus of claim 2, wherein said primary roller is made of steel of a hardness greater than 50 Rockwell C.
 4. The crushing apparatus of claim 3, wherein said secondary rollers are also of resilient steel of a hardness greater than 50 Rockwell C.
 5. The crushing apparatus of claim 2, wherein said roller rotation means rotates said rollers at a peripheral velocity that is in the range of 5 to 9 meters/sec.
 6. Apparatus for crushing particulate materials, comprising: a primary crushing roller of a first diameter, said primary roller having an axis which is generally horizontal and said primary roller having a peripheral surface; two secondary rollers, said secondary rollers each having an axis parallel to said primary roller axis, and each having a respective peripheral surface which is in engagement with said primary roller peripheral surface; said secondary roller peripheral surfaces being spaced apart a first distance less than said fIrst diameter; said secondary rollers being located one above the other and being located such that materials passing between said primary and the upper said secondary rollers will fall and be directed by rotation of said rollers to move between said primary and the lower said secondary rollers; means for rotating said rollers about their respective said axes to direct the material to move between the upper said secondary roller and said primary roller and thereafter to move between the lower said secondary roller and said primary roller; said primary roller axis being offset from a line joining said secondary roller axes; said first distance between said secondary rollers and said primary roller first diameter being selected so that said primary roller peripheral surface extends toward, but does not cross, the line joining said secondary roller axes; the angle defined by the upper said secondary roller axis, said primary roller axis and the lower said secondary roller axis is greater than 90*; each said secondary roller has a diameter that is in the range of from 1.5 to 4 times greater than said primary roller diameter.
 7. The crushing apparatus of claim 6, wherein said primary roller diameter is in the range of from 80 to 250 mm.
 8. Apparatus for crushing particulate materials, comprising: a primary crushing roller of a first diameter, said primary roller having an axis which is generally horizontal and said primary roller having a peripheral surface; said primary roller is comprised of resilient material, which is depressed as material to be crushed passes between said primary and an upper secondary roller and which resiliently restores itself afterward to expel the crushed material from said primary roller; two secondary rollers, said secondary rollers each and each having an axis parallel to said primary roller axis, and each having a respective peripheral surface which is in engagement with said primary roller peripheral surface; said secondary roller peripheral surfaces being spaced apart a first distance less than said first diameter; said secondary rollers being located one above the other and being located such that materials passing between said primary and the upper said secondary rollers will fall and be directed by rotation of said rollers to move between said primary and the lower said secondary rollers; means for rotating said rollers about their respective said axes to direct the material to move between the upper said secondary roller and said primary roller and thereafter to move between the lower said secondary roller and said primary roller.
 9. The crushing apparatus of claim 8, wherein said roller rotation means rotates said rollers at a peripheral velocity that is in the range of 5 to 9 meters/sec.
 10. The crushing apparatus of claim 9, wherein said primary roller is made of steel of a hardness greater than 50 Rockwell C., said secondary rollers also being of resilient steel of a hardness greater than 50 Rockwell C.
 11. The crushing apparatus of claim 10, wherein the angle defined by the upper said secondary roller axis, said primary roller axis and the lower said secondary roller axis is greater than 90*.
 12. A PROCESS FOR CRUSHING PARTICLES OF HARD MATERIAL COMPRISING THE STEPS OF: PROVIDING TWO PARALLEL VERTICALLY SPACED APART SECONDARY ROLLERS AND A PRIMARY ROLLERS DISPOSED ADJACENT THE SPACE BETWEEN THE SECONDARY ROLLERS AND CONTACTING BOTH OF THEM, FORCING THE PRIMARY ROLLER SIMULTANEOUSLY AGAINST BOTH SECONDARY ROLLERS, ROTATING THE PRIMARY ROLLER IN A DIRECTION WHICH MOVES MATERIAL BETWEEN THE PRIMARY AND UPPER SECONDARY ROLLER, ROTATING THE SECONDARY ROLLERS IN THE OPPOSITE DIRECTION, FEEDING MATERIAL TO BE CRUSHED AT A PREDETERMINED FLOW RATE TO A LOCATION FROM WHICH IT CAN MOVE BETWEEN THE UPPER SECONDARY AND PRIMARY ROLLERS, CRUSHING THAT MATERIAL BETWEEN THE UPPER SECONDARY AND PRIMARY ROLLERS, THROWING THE CRUSHED MATERIAL OFF THE PRIMARY ROLLER AFTER THE MATERIAL TO BE CRUSHED HAS MOVED BETWEEN THE UPPER
 13. The process for crushing material of claim 12, wherein the primary and secondary rollers are rotated at the same peripheral velocity.
 14. The process for crushing material of claim 13, wherein the crushed material is thrown from the primary roller by selecting a primary roller of sufficient resiliency and by selection of a roller peripheral speed coordinated with the roller resiliency to be sufficient to throw off the material.
 15. The process for crushing material of claim 14, wherein the roller peripheral velocity is in the range of from 5 to 9 meters/sec.
 16. The process for crushing material of claim 14, wherein the granulometric spectrum of the particles produced by crushing is adjusted first by selecting an appropriate hardness and resilience for the roller material and by selecting an appropriate number of rollers and by selecting a predetermined rotation speed for the rollers and thereafter by performing only at least one of the steps of: changing the diameter of the primary roller with respect to the diameter of the secondary rollers, changing the pressure exerted by the primary roller and changing the rate of feed of particles of material to the primary and upper secondary roller. 